The present invention relates to a method for steering saw blades and a saw blade steering apparatus constructed in accordance with the teachings of the method; the method and apparatus having particular application in milling wood cants of irregular shape.
U.S. Pat. No. 5,722,474 (Raybon et al) entitled xe2x80x9cMethod and apparatus for cutting a cant into boardsxe2x80x9d and U.S. Pat. Nos. 5,761,979 and 5,870,936 (McGehee) (Canadian equivalent 2,198,662) both entitled xe2x80x9cEdge trimming and board ripping apparatus and methodxe2x80x9d relate to the processing of wood cants of irregular shape. The objective is to facilitate high speed sawing of wood cants of irregular shape into dimensionally similar portions of sawn lumber for the purpose of maximizing solid lumber recovery.
The preferred method described in McGehee involves the steps of: 1) scanning a wood cant to determine a cutting pattern; 2) directing the wood cant through a saw assembly consisting of saw blades mounted on and rotated by a rotating arbor; 3) adjusting in unison the skew angle of the saw blade axis of each of the saw blades relative to the arbor axis, with such adjustments being carried out while the saw blades are rotated by the arbor in order to cut the wood cant according to the cutting pattern determined by scanning step. As the skew angle of the saw blades is adjusted, the lateral position of the saw blades in relation to a centerline of the blade supports is altered. The operation is computer controlled with this lateral offset of the saw blades accommodated in the programming of the computer.
A limiting factor in applying the teachings of the McGehee method is in the saw blade steering apparatus used to adjust in unison the skew angle of the saw blades. Existing apparatus are expensive to manufacture and maintain, due to their complexity.
What is required is an alternative method and apparatus for steering saw blades.
According to one aspect of the present invention there is provided a method for steering saw blades. A first step involves providing an arbor rotatable about a rotation axis. A second step involves mounting saw blades on the arbor in such a manner that the saw blades rotate with the arbor and are angularly adjustable in relation to the rotation axis of the arbor. A third step involves providing a rigid guide assembly having a plurality of guides each of which accommodate one the saw blades, such that movement of the guide assembly moves the saw blades in unison. A leading edge of each of the saw blades is positioned along a common alignment plane. A fourth step involves providing a support for the guide assembly having an underlying pivot axis spaced from and substantially perpendicular to the rotational axis of the arbor. The pivot axis is on the alignment plane such that the leading edge of each of the saw blades remain positioned along the alignment plane as the guide assembly is pivoted to move the guide assembly to alter the angular positioning of the saw blades.
According to another aspect of the present invention there is provided an apparatus for steering saw blades which includes an arbor rotatable about a rotation axis. Saw blades are mounted on the arbor in such a manner that the saw blades rotate with the arbor and are angularly adjustable in relation to the rotation axis of the arbor. A rigid guide assembly is provided having a plurality of guides each of which accommodate one the saw blades, such that movement of the guide assembly angularly adjusts the saw blades in unison. A leading edge of each of the saw blades is positioned along a common alignment plane. A support is provided for the guide assembly. The support has an underlying pivot axis spaced from and substantially perpendicular to the rotational axis of the arbor. This pivot axis is on the alignment plane such that the leading edge of each of the saw blades remain positioned along the alignment plane as the guide assembly is pivoted to move the guide assembly to alter the angular positioning of the saw blades.
The method and apparatus for steering saw blades disclosed in the McGehee et al patent reference the leading edge of the saw blades are a substantial distance away from the pivot point of the guides. This creates a lateral offset of the saw blades when the guides are angularly pivoted which must be continually compensated for through computer programming to ensure correct positioning. With the above described method and apparatus, this issue is addressed by placing the pivot axis for the guide support directly below and in line with an alignment plane for the leading edge of the saw blades. The saw blades have negligible laterally movement relative to the alignment plane during left or right rotation of the guide support. This greatly reduces the amount of calculations required from the computer and simplifies the programming required to operate the system. Not having to account for lateral offset also increases the accuracy of the sawing.
The method and apparatus for steering saw blades disclosed in the McGehee et al patent reference utilizes a group of guides which are individually pinned so that each guide must slide against the adjacent guide in the group in order to pivot on it""s own axis. Wear resulting from this sliding friction between the guides is addressed by providing for porting for pressure lubrication between the sliding guide surfaces and by hardening the guide surfaces. These measures serve to increase the cost of the guide system. With the above described method and apparatus, the guides are maintained as a rigid assembly and are pivoted as a group. This eliminates the need for a pressure lubrication system since the guides do not slide against one another. Guide construction is simplified and the guides can be made from conventional materials.